Methionine and aqueous solutions of methionine salts, in particular sodium methioninate (DE 31 05 009 C), but also substitutes such as the methionine hydroxy analogue (MHA) are used all over the world as feed additives for rearing poultry, pigs and other economically useful animals and mainly promotes the production of animal protein. With regard to the increasing population of the world and increasing nutritional problems, methionine, as one of the essential amino acids in the animal growth process, and its different forms, and thus also its cost effective production, are very important. Solid or liquid forms may be preferred, depending on the requirements.
Commercially available sodium methioninate solution has a concentration of 40 wt. % methionine and its biological value corresponds to that of solid methionine, in contrast to the substitute MHA, compared on an equimolar basis. There are several suitable methods for preparing these types of sodium methioninate solutions, e.g.:
1. Dissolution of isolated methionine in caustic soda solution. PA1 2. Alkaline hydrolysis of 5-(.beta.-methylmercaptoethyl)-hydantoin with NaOH and/or Na.sub.2 CO.sub.3. PA1 3. Alkaline hydrolysis of methionine amide. PA1 1. It has precisely the same nutritive efficacy as solid crystalline methionine. PA1 2. It can be converted into a liquid form at the desired concentration by the feedstuff mixer itself, without having to handle, for example, alkalis. PA1 3. As little as possible "dead volume" in the form of water is carried during transport, so that the active substance content of the transported material is high. PA1 4. The product can be adapted to the specific requirements of the individual users and optionally may also be used as a solid. PA1 a) free-flowing character and ease of handling PA1 b) reduced dust content, PA1 c) reduced tendency to cake when exposed to the weather PA1 d) high bulk density.
Although method 1 provides the purest product it is more costly and thus less economic than the production of methionine itself, due to an additional process step in comparison to production of the solid. In contrast, methods 2 and 3 are used at an earlier point in the production of methionine and thus there is no need to isolate the solid during the production of DL-methionine, depending on capacity.
The preparation of 5-(.beta.-methylmercaptoethyl)-hydantoin is performed in a known manner by direct synthesis from the conventional starting materials methylmercapto-propionaldehyde (MMP) and hydrocyanic acid in the presence of ammonia and carbon dioxide. Methionine amide is prepared in a known manner by hydrolysis of methionine nitrile, which again is obtained by direct synthesis from the conventional starting materials MMP, hydrocyanic acid or ammonium cyanide and ammonia.
Depending on special requirements, it may be expedient to use a solid or a liquid form of the animal feed supplement.
The decision about which form to produce depends, inter alia, on the mixing apparatus which is available and the specific preferences of the particular manufacturer.
When preparing mixed feeds, the different feedstuffs and additives are initially present as separate components which, depending on their characteristics, are prepared by milling, shredding, drying or purifying. If the separate components have the characteristics required, the actual mixing process is performed in a mixing unit suitable for this process. Individual mixed batches differ, depending on the size of the unit. The essential amino acid methionine is used as a supplement for mixed feeds in concentrations of the order of magnitude of 0.01 to 1.0 wt. %. These amounts are added directly to the mixed feed by appropriate weighing and metering systems.
DE 31 05 009 describes the fact that aqueous solutions of sodium or potassium methioninate have the same methionine activity as solid methionine when used as an animal feed additive.
However, a result of the low-temperature stability of methioninate solutions, which has to be guaranteed by suppliers, it has hitherto been possible to supply only solutions with a concentration of up 40 wt. % of methioninate. Thus commercial products contain up to about 60 wt. % of water which leads to an approximately 2.5-fold increase in transport costs as compared with the transport of solid methionine. This has prevented liquid supplements based on methionine penetrating the market.
The use of crystalline sodium methioninate has not been considered due to the strongly hygroscopic nature of this compound.
However, it would be very useful to provide an additive for animal feeds which satisfies the following requirements: